Urban centres are vulnerable to remote threats (terrorism, climate
change, the spread of disease), yet there are few tools available to
assess these problems. We propose a preliminary framework to assess the
vulnerability of urban systems to future shocks based on landscape
ecology's "Panarchy Framework." According to Panarchy,
ecosystem vulnerability is determined by three generic characteristics:
(1) the wealth available in the system, (2) how connected the system is,
and (3) how much diversity exists in the system. In this framework,
wealthy, non-diverse, tightly connected systems are highly vulnerable.
The wealth of urban systems can be measured using the approach pioneered
by development economists to assess how poverty affects food security.
Diversity can be measured using the tools investors use to measure the
diversity of investment portfolios to assess financial risk. The
connectivity of a system can be evaluated with the tools chemists use to
assess the pathways chemicals use to flow through the environment. This
approach can lead to better tools for creating policy designed to reduce
vulnerability, and can help urban or regional planners identify where
systems are vulnerable to shocks and disturbances that may occur in the
future.

Some threats that cities face, such as earthquakes, can be dealt
with through the technical expertise of the engineers who build the
infrastructure that physically surrounds us (American Society of Civil
Engineers, 2003). The events of September 11th and the SARS outbreak,
however, emphasize that despite our best technical efforts urban centers
remain vulnerable to remote threats that are impossible to predict. This
has led both journalists and academics to consider urban security in a
new light. For example, some scholars suggest that global
transportation, energy, information and economic systems are so
interwoven that these systems are fundamentally vulnerable. Problems can
quickly spread, cascading to create ever-increasing levels of chaos in
urban regions (Homer-Dixon, 2002). Predicting these types of
"global" threats and anticipating how urban systems will
respond is difficult because the complex interrelated systems that
support urban society behave in inherently unpredictable ways (Bar-Yam,
1992; Holland, 1995; Kauffman, 1995; Waldrop, 1992; Williams, 1997).
Addressing these sorts of problems is not commonly associated with urban
planning, which traditionally deals with issues that tend to stop at the
town border. Nevertheless, urban boundaries are porous to the threats
that dominate today (climate change, terrorism, the spread of disease
from remote locations), so it is helpful to situate the city in a
broader socio-economic and biophysical context. This allows us to
establish a basic framework for understanding remote and complex
threats. Armed with this framework we can begin building tools that may
be useful to the urban planning community to assess whether individual
cities have the capacity to withstand major disturbances. It must be
acknowledged, however, that this level of planning, which goes far
beyond urban areas, also goes beyond the responsibility of urban
planners and must include regional planners and even higher
administrative levels of policy development.

One set of tools to address these sort of risks are top-down
modeling driven approaches. These include the global circulation models
used to predict climate change. Due to scientific uncertainty, it has
not been possible thus far to apply these models effectively at the
regional level. (Cline, 1996; Intergovernmental Panel on Climate Change,
2001a, 2001b; Kandlikar & Risbey, 2000; Mendelsohn, Nordhaus, &
Shaw, 1994; Reilly, 1999; Reilly, Hohmann, & Kane, 1994). Even
general trends can be difficult to predict. For instance, there is
considerable disagreement on the potential impacts of world trade: some
models predict that economic globalization will lead to inequality and
environmental degradation, while others conclude that it is our best
tool for reducing poverty and conserving rare species (Bradshaw &
Smit, 1999; Ervin, 1997; Greunspecht, 1996; Halweil, 2002; Potter,
2000). The difficulty with this top-down approach is that it requires
good data from all parts of the globe, and the quality of data varies
tremendously from location to location. Another problem is that the
complexity of these systems eludes our best modeling attempts.

A different approach is to assess whether a community has the
capacity to adapt to change rather than trying to predict change itself.
This has led to definitions of resilient communities and
characterizations of communities that possess social capital (Berkes
& Folke, 1998; Boggs, 2001; Carpenter, Walker, Anderies, & Abel,
2001; Pretty, 2003; Putnam, 2000). Although academically interesting,
this kind of "bottom-up" approach implies that everything
ecological, social and political must be considered (Yohe & Tol,
2002). The result is a mass of information that is too complex to
provide useful policy making tools (Fraser, Mabee, & Slaymaker,
2003) and it is unclear how we can separate useful and relevant
information from that which is merely superfluous or anecdotal.

To find a balance between the overly complex and the simplistic, we
propose applying a set of principles derived from the field of landscape
ecology to help expose vulnerability in urban systems. Landscape ecology
is relevant because most ecosystems experience disturbances such as
forest fires, windstorms and pest outbreaks (Attwill, 1994). While the
timing and nature of these disturbances are difficult to predict, the
impact of a disturbance always depends on three key general
characteristics of the ecosystem: the wealth present in the system, the
connectivity of individuals within the system as well as the
connectivity between systems, and the diversity associated with the
system (Gunderson, Holling, & Peterson, 2002; Gunderson &
Holling, 2002; Holling, 2001). For example, the impact of a forest fire
will be dictated by the amount of fuel available for the fire to consume
(wealth), the forest's linkages to other resources (connectivity),
and the age and species distribution of the flora and fauna being
destroyed (diversity). A fire in a large, mature forest that is densely
planted and only made up of a few species will have greater impact than
a fire in a remote, small, and poorly stocked forest; thus, the former
system is more vulnerable to the threat of fire than the latter.

While these three characteristics were first used to describe
ecological systems, there is some evidence to suggest they can be
effectively applied to human networks as well. The Irish Potato Famine,
for instance, resulted when a large number of communities depended
entirely on an agro-ecosystem that was biologically wealthy, closely
connected and had low diversity (Fraser, 2003). Forest fires that occur
in close proximity to human settlement, such as the wildfires in
California or British Columbia, have much greater economic impact than
do remote disturbances. This framework has also been used to draw
parallels between the development of human networks, such as the Hindu
caste system, and the evolution of ecosystems (Berkes & Folke,
2002).

Diversity is probably the easiest of the three characteristics to
apply to urban systems. For example, for the cities of the Western
world, our primary source of food comes from grain production, which is
situated far from the city in a non-diverse agricultural system that
specializes in a very small number of genetically similar crops. By
their very nature, the agro-ecosystems that cities depend on are
vulnerable since biologically diverse agricultural systems are better
able to withstand pest outbreaks than simple ones (Altieri, 1999;
Benbrook, 1990; Gliessman, 1998; Mannion, 1995). This system
vulnerability has led international bodies such as the United Nations
Global Environment Fund and the International Development Research
Council to call for greater diversity in the food systems (Global
Environment Facility, 2000; IDRC, 1992). To apply this to urban
planning, it is necessary to understand the various ways that a city
obtains its basic requirements such as food. If this is deemed to be too
highly specialized urban planners can take steps to diversify these
systems (see Figge (2002, 2004) for a methodological discussion on how
to identify risk in terms of diversity in the food system). In the case
of the food system, promoting urban or peri-urban agriculture could do
this. Although not as common in the Western world, where urban
agriculture is mostly associated with specific cultural groups who have
a strong traditional ties with gardening (Fraser & Kenney, 2000),
urban agriculture is an extremely important component of urban
livelihoods in the developing world, especially amongst poorer
communities (Brook & Davila, 2000; Fraser, 2002a; Maxwell, Levin,
& Csete, 1998).

If a system is tightly connected to the region around it,
disturbances can quickly spread and an area will be vulnerable to remote
threats. The 2003 SARS outbreak in Ontario illustrates this point, as
Toronto's medical system was thrown into chaos because of a chance
occurrence in rural China when a virus jumped from a cat to a human. One
way to assess connectivity is to evaluate the various pathways of
material, labour and capital that flow through an urban region. By
tracking these pathways, it may be possible to safeguard cities by
changing our practices at the source. For example, in Walkerton,
Ontario, seven people died and an estimated 2300 became ill when
bacteria infected drinking water in the spring of 2000. Although the
problem was eventually blamed on failures in the water safety system
(Hrudey, Huck, Payment, Gillham, & Hrudey, 2002), the source of the
problem was the connection between livestock faeces and municipal wells.
Manure had been spread on fields overlying a shallow aquifer near one of
the town's wells immediately prior to an intense spring rainfall
(O'Connor, 2002). The rain soaked fields provided a transport
mechanism that carried the pathogens through the soil and into the
groundwater source. Ironically, municipal planners had long been aware
of the connection between drinking water quality and surface
agricultural activities, but recent changes in water quality monitoring
created an opportunity for the threat to translate into a catastrophe.

Wealth, which landscape ecologists consider a characteristic of
vulnerability, is the most difficult to apply to an urban setting. When
used in an ecological context, wealth refers to a rich supply of biomass
that is attractive to opportunistic pests (Holling, 2001). This is
similar to some wealthy trans-national corporations that may be less
able to innovate and adapt to new circumstances than smaller, less
wealthy organizations (Homer-Dixon, 2000; Saul, 1993). However,
financial wealth can also reduce vulnerability. For example, rich
communities are better able to afford houses that do not collapse during
earthquakes. Therefore, to apply wealth as a characteristic of
vulnerability, we must first distinguish between biologically wealthy
ecosystems, where wealth indicates a vulnerable system, and human
systems where wealth can help build adaptability. We must then assess
whether an organization is so large and entrenched that it is unable to
use its wealth to find novel solutions to changing conditions.

Policy makers and planners can use this framework, and characterize
urban systems in terms of wealth, diversity and connectivity, to expose
areas where our society is vulnerable to unanticipated threats. For
example, our food system is extremely efficient and provides urban
residents with abundant low-cost and high quality food. One reason that
food production is so efficient, however, is that crops are produced in
tightly connected, biologically wealthy and non-diverse farms. The
simplicity and connectivity of this system allows farmers to plant, tend
and harvest vast areas of one crop, maximizing biological productivity
(Friedland, 1994; Friedland, Barton, & Thomas, 1981). Crops can then
be gathered, processed, turned into food and shipped at low economic
cost due to the high connectivity and low diversity in the system. The
tremendous wealth in this system is also partly due to the fact that
regions specialize in producing only those commodities that they have a
comparative advantage in (Gillis, Perkins, Roemer, & Snodgrass,
1992; McCalla & Josling, 1985). This example has all the traits of a
vulnerable system with a limited capacity to respond to shocks.

This leads to a number of policy implications; to reduce
vulnerability, planners can ensure that urban regions have access to
local food producing regions, which would diversify food sources in the
case of a failure. Maintaining local agricultural capacity, however, is
controversial as small scale farms on the periphery of major cities are
often uneconomical because they cannot compete with major food producing
regions (Fraser, 2002b, Submitted). Planners are, therefore, faced with
a trade-off: at what point is it ok to sacrifice resilience in favour of
a larger-scale, more efficient system to provide us services? Economic
realities have driven society to create systems that do not have
unnecessary duplication in many different regions, and achieve economies
of scale by situating key activities in those regions where activities
can be done at the least cost. Conversely, planners must also design
systems with adequate backups, or redundancies, so that if a key node in
the system is damaged, lives and livelihoods are not too affected. The
need to achieve a balance between efficiency and security in a world
dominated by complex global systems creates a tension for planners that
cannot be addressed with tools presently available.

This conundrum is exemplified by North America's power system,
which is so centralized and tightly coupled that failure of a generator
in Ohio in the summer of 2003 led to system collapse and blackouts
across a huge area of Canada and the United States. Decentralizing the
system, thereby reducing connectivity, may be the best way of reducing
vulnerability, however, may lead to even greater problems. (2)

The benefit of using this framework from landscape ecology is that
it can reduce the number of variables under consideration, which makes
the remaining information more useful in developing a planning tool. It
is only a framework, however, not a predictive model, and as such makes
no attempt to anticipate when, where or in what form a problem might
materialize. The authors feel that this approach provides a certain
degree of guidance in understanding systems that may be at risk even
though they appear robust on the surface. It is also a way of relating
remote, distant or removed threats specifically to the urban systems
that planners are responsible for. If used, therefore, this approach
should be considered a way of flagging troublesome areas for careful
study and analysis. However, any policy decision to address these
problems will require the input of a number of administrative levels
since the origin of these sorts of problems is not the responsibility of
urban planners who must deal with more local issues such as
infrastructure, land use, waste management and the transportation
system.

This is not an attempt to predict how events on the far side of the
world will affect the cities where we live. We can take it as a given
that far away occurrences will impact us in strange and unpredictable
ways. Rather, this is an attempt to understand the characteristics of
vulnerability, so that we can pro-actively recognize communities that
may be adversely affected. By identifying these characteristics, we also
identify characteristics of resilience. This, therefore, should lead us
to better policy: a good policy is one that moves us away from
vulnerability and towards resilience.

Acknowledgments

Many thanks to Olav Slaymaker and Lloyd Axworthy for on-going
support and discussions on this topic and to the two anonymous reviewers
who provided input into the manuscript. Thanks also to Herb Barbolet,
Kathleen Gibson, Lawrence Alexander and Kristina Bouris (the Growing
Green Team) for great collaboration on food systems. This research
program was established through the generous support of the Simons
Foundation at the Liu Institute for Global Issues, University of British
Columbia and the Government of Canada's Voluntary Sector
Initiative.

Notes

(1) The framework laid out here is preliminary and represents the
first steps on a much longer research programme begun at the University
of British Columbia, and now currently being followed through at the
University of Leeds in the UK.

(2) For example the power system in rural Belize, Central America
is so decentralized that everyone who can afford a diesel generator owns
one (this observation was based on personal experience during fieldwork
in 1997). Although this system is so diverse and unconnected that a
system-wide collapse is almost impossible to imagine, this is a highly
inefficient, polluting and noisy way of generating power.

References

Altieri, M. 1999. Enhancing the Productivity of Latin American
Traditional Peasant Farming Systems. Paper presented at the Sustainable
Agriculture: An Evolution of New Paradigms and Old Practices, Bellagio
Centre April 26-30.

American Society of Civil Engineers. 2003. Publications on the
Vulnerability and Protection of Infrastructure Systems. American Society
of Civil Engineers. http://ascestore.aip.org/OA_HTML/asce_ciriac_abs.jsp
(Accessed October 23, 2003).

Bradshaw, B., and B. Smit. 1999. Banking on the Downturns and
Capitalizing on the Upturns: the dual implications of deregulation for
farm-level resource use. Paper presented at the International Geographic
Union's Commission on the Sustainability of Rural Systems
Conference: The Reshaping of Rural Ecologies, Economies and Communities,
Simon Fraser University, Burnaby, British Columbia, Canada.

Fraser, E. 2002b. Ecologies of Scale: Socio-economic obstacles to
sustainable agriculture in the Lower Fraser Valley. Ph.D diss.,
University of British Columbia, Vancouver.

Fraser, E. 2003. Social vulnerability and ecological fragility:
building bridges between social and natural sciences using the Irish
Potato Famine as a case study. Conservation Ecology 7(1): 9 on line.

Fraser, E. n.d.. International trade, agriculture, and the
environment: the effect of freer trade on farm management and
sustainable agriculture in southwestern British Columbia, Canada.
Agriculture and Human Values, Under Review.

Fraser, E., and A. Kenney. 2000. Cultural factors and landscape
history affecting perceptions of the urban forest. The Journal of
Arboriculture 26(2): 107-113.